1. Field of the Invention
The present invention relates to analysis technology involved in gene sequences in analyses of biologically functional molecules, particularly DNA sequences and in genetic diagnosis, and a method for manufacturing a substrate for making a device for analysis used for those analyses.
2. Description of the Related Art
Analysis of DNA sequences of genes represented by the analysis of human genome has undergone a rapid progress recently, and the information obtained by such analyses has been applied vigorously to the investigation of the functions of genes, and diagnosis of gene-mediated diseases. In parallel with this tendency, many researches have been performed on so-called DNA chips or DNA microarrays, because those chips are a powerful tool for the technique which allows the rapid and large-scale analysis of genes or study of the functions of genes.
The DNA microarray is an element wherein each of DNA molecules having specified sequences is immobilized on a tiny space so that a DNA strand in a sample having a sequence complimentary to a specified sequence can be detected. CHEMTECH, February 1997, pp. 22 proposes a method for manufacturing a DNA array based on photolithography conventionally used for the fabrication of semiconductors, wherein the site-selective synthesis of DNA sequences is carried out through a process of multiple steps so that a microarray modified by a variety of DNA molecules can be prepared after a surprisingly small number of processes. This document suggests the possibility of preparing a microarray that will allow one to examine one billion or more different kinds of DNA sequences at one time by repeating the 15-time hybridization of different nucleotides site-selectively and systematically.
On the other hand, if it were possible to electrically detect a DNA strand complimentary to a specified sequence as described above, it would be possible to analyze DNA sequences by a rapid and simple method. A number of attempts have been made for producing semiconductor apparatuses allowing for the electric detection of a DNA strand and as such known attempts, can be mentioned Domestic Re-publication of WO2003/087798 and Japanese Patent Laid-open (Kokai) No. 2005-77210. In these semiconductor apparatuses, the presence or absence of the complementary DNA strand is detected on a microchip as a practical application of a sensor by a field effect transistor known conventionally.
Incidentally, in order to prepare a DNA microarray enabling the rapid and large-scale analysis, it is necessary to immobilize DNA strands onto the tiny space of a microarray substrate site-selectively so securely that no such problems as detachment and the like can never arise. In order to analyze the biologically functional molecules including DNA molecules, as the method for two-dimensionally immobilizing them on a metal, the method of using specific absorption of a sulfur atom on a gold surface is known and described in, for example, Domestic Re-publication of WO2003/087798. Alternatively, there has been a method known for a considerably long period of time that consists of forming a monomolecular film on the surface of a substrate using silicon oxide chains, and immobilizing enzymes to the alkyl chains extending from silicon atoms in such a manner as to allow the enzymes to be immobilized to the semiconductor so securely that the risk of the molecules thus immobilized of being subject to detachment can be minimized, and Japanese Patent Laid-open (Kokai) No. 62-50657 discloses one such method. The above-mentioned Japanese Patent Laid-open (Kokai) No. 2005-77210 also mentions this method can be applied to the method it deals with.
When immobilize a material for the detection material such as a DNA molecule or peptide is immobilized onto the surface of a substrate for making a microarray, it is advisable to resort to the above-described method based on a monomolecular film comprising silicon oxide chains because the method will ensure the formation of a film comparatively free from the problems such as detachment as described above.
When it is desired to prepare a high-performance microarray, it will be necessary to achieve the site-selective immobilization of a material utilizing microlithography as indicated in CHEMTECH, February 1997, pp. 22. However, such microlithography as shown in CHEMTECH, February 1997, pp. 22 is complicated and expensive. Therefore, there is a need for a substrate for making a microarray that will allow the low-cost production and secure site-selective immobilization of a material thereto.
When it is required to immobilize a material for the detection material such as a DNA molecule or peptide on the surface of a substrate that incorporates a field effect transistor as a DNA sensor, the above-described method based on the use of a monomolecular film comprising silicon oxide chains will ensure the secure immobilization, because the method will allow the substrate to be stably placed in close proximity to the probe.